Fix Magento_ImportExport not supporting unicode characters in column names

Author: tdgroot

app/code/Magento/ImportExport/Model/Import/AbstractEntity.php

@@ -831,7 +831,7 @@ public function validateData()
                 if (!$this->isAttributeParticular($columnName)) {
                     if (trim($columnName) == '') {
                         $emptyHeaderColumns[] = $columnNumber;
-                    } elseif (!preg_match('/^[a-z][a-z0-9_]*$/', $columnName)) {
+                    } elseif (!preg_match('/^[a-z][\w]*$/u', $columnName)) {
                         $invalidColumns[] = $columnName;
                     } elseif ($this->needColumnCheck && !in_array($columnName, $this->getValidColumnNames())) {
                         $invalidAttributes[] = $columnName;

app/code/Magento/ImportExport/Model/Import/Entity/AbstractEntity.php

@@ -803,7 +803,7 @@ public function validateData()
                     if (!$this->isAttributeParticular($columnName)) {
                         if (trim($columnName) == '') {
                             $emptyHeaderColumns[] = $columnNumber;
-                        } elseif (!preg_match('/^[a-z][a-z0-9_]*$/', $columnName)) {
+                        } elseif (!preg_match('/^[a-z][\w]*$/u', $columnName)) {
                             $invalidColumns[] = $columnName;
                         } elseif ($this->needColumnCheck && !in_array($columnName, $this->getValidColumnNames())) {
                             $invalidAttributes[] = $columnName;